Safety control system for hot wire ignition in fluid fuel burners



NOV. 29, 1932. MccABE 1,889,448

SAFETY CONTROL SYSTEM FOR HOT WIRE IGNITION IN FLUID FUEL BURNERS Filed Feb. 7. 1930 4 Sheets-Sheet 1 INVENTOR M IRA E.MCCAE E v BY M M ATTORN EY NOV .1932. L cc 1,889,448

SAFETY CONTROL SYSTEM FOR HOT WIRE IGNITION IN FLUID FUEL BURNERS Filed Feb. 7. 19 50 4 Sheets-Sheet 2 N o INVENTOR [RA E. M CREE TORNEY Nov. 29, 1932. 1. E. MOCABE 1,889,448

SAFETY CONTROL SYSTEM FOR HOT WIRE IGNITION IN FLUID FUEL BURNERS 4 Sheets-Sheet 5 Filed Feb. 7. 1950 INVENTOR IRA E. M CABE ATTORNEY URNERS l. E- M CABE Nov. 29, 1932.

SAFETY CONTROL SYSTEM FOR HOT WIRE IGNITION IN FLUID FUEL B Filed Feb. 7, 1930 4 Sheets-Sheet 4 INVENTOR IRA ELM CABE x M ATTORN EY Patented Nov. 29, 1932 UNITED STATES- PATENT OFFICE 7 "ma a. means, or cnrcaoo, minors v v Q r sunrrcomapr. srsrnu FOB nor wnm IGNITION in non) roan BUBNERS k Application filed February 7, 1930. 8erlal 170.4%,521.

This invention'relates to a safety control for an electrically operated domestic fuel burner of the type which employs an mcandescent wire to initiate combustion ofthe uid fuel.

It is an objectof this invention to provide a system of-the character described in which the elements are so constructed and arranged that a current of constant intensity is pro-- 9 vlded for heating the ignition wire to incandescency irrespective of the fluctuations of the commercial current; to rovide a definite period for the preheating o the ignition wire descency before fuel can be delivered and thereafter continue the incandescence of the wire for a predetermined period, for the purpose of i iting the fuel, andin case of the failureo or thermally actuated devices for closing the motor circuit, the fuel burner will remain inoperative.

The advantages of this system are, that in case 1: e fuel fails to ignite initially the motor will be shut down and manually reset before the device can be operated. If the burner flame fails after come bastion has been initiated, the motor is immediately shut down and the device recycles so that if the cause of the failure hasbeen' removed the burner will again be operated and if the cause has not been removed, the burner will not be again operated until the device is manually reset.

case of a temporary failure of the commercial circuit, the motor is immediately shut down and the device recycles, so that if, during the recycling period, the commercial current has resumed, the burner will resume operation. 1 7

With these and other objects in view, reference is made to the accompanying sheets of drawings illustrating a preferred embodiment of this invention, with the understanding that minor detailed changes may be made without departing from the scope thereof.

In the drawings: 7

igure 1 is a wiring diagram illustrating an em ent of this invention.

Figure2 is an enlarged detailed view in front elevation of the control panel which plated by either the electrically operated the device must be boiler and normally remains mounts certain devices diagrammatically illustrated in Figure 1.

Figure 3 is a fra entary view partly in vertical central section and artly in sideelevation of an application of thisdevice to a rotary type of fluid fuel burner as installed in a omestic heater or furnace.

Figure 4 is an enlarged detail top plan view of one form of ignition wire as contemplated by this invention.

Figure 5 is a view in front elevation and Figure 6 is a view in side elevation of Figure 4. c

Figure 7 is a view in frontelevation of a modified form of ignition wire as contemthis invention.

Referring to Figure 1, in electrically operated fluid fuel burners for domestic purposes, it is customary that the motor for operating the same is connected to the commercial -or electric lighting system of the dwellmg or place in which the burner is installed.

Figure 1- illustrates the incoming commerclal current passing through a room thermostat R, of commercial construction, thence through a boiler control B, of commercial construction, to the binding post 1 upon the and thence through a safety the binding post 4 in a thermal switch TS or stack safety of commercial preferably of the .type illustrated and described in my prior pending application Serial No. 311,436, filed Octobe Patent No. 1,762,183 of June room thermostat R and boiler control B are hot shown in closed positions. It is customary in fluid fuel burners to employ both of these devices, the room thermostat being located in the portion of the building where a predetermined uniform tem perature is desired and will operate to close the circuit when the temperature has descended below the desired degree. The boiler control Bis attached to the furnace or closed, but will open whenever the conditions within the boiler approach the danger line. The ther- 10, 1930. The

construction,-

r 10, 1928, now,

mal safety TS includes two mercury tube V windings of the solenoid A to the binding binding post switches 5 and 6 and are so supporte upon the operating mechanism that when one switch is 0 en the other switch is closed, and

" when'tilte to reverse the relations, the open switch will be closed before the closed switch is opened and vice versa. The switches in the thermal switch in Figure 1 are shown in the positions assumed when the furnace is cold. The safety switch S is also of commercial construction and is preferably constructed in the manner illustrated and described in my prior Patent No. 1,648,389 of Nov. 8,1927. As shown in Figure 1 this switch is normally closed. The mercury switch tube 3 is tiltably mounted upon the upper side of a solenoid A, which is of commercial construction, and includes a dashpot D for retarding the movement of the solenoid core C. The switch 3 is so mounted that when the solenoid is energized, the upward movement of the core C will tilt the switch. Figure 1 illustrates the mercury tube switch 3 in open position, which is the position assumed when the solenoid is deenergized, so that in this position no current passes from binding post 2 through switch 3.

The incoming current having been traced through binding post 1, safety switch S,

2, to binding post 4 in the thermal switch and as the switch tube 5 is shown in closed position, the current passes therethrough to the binding post 7 and thence to the binding post 8. Here the current branches, a. portion of it passing through the post 9 and thence back to'the commercial line, the other portion passing from binding post 8 through the primary coil PC of the transformer T and thence through binding post 9 back to the commercial line. The transformer T is constructed as shown and described inmy prior pending application Serial No. 331,542, filed Jan. 10, 1929. The

- energizing of the coil of the solenoid A causes the core to rise upward, the action of which is delayed by a dashpot,,unti1 the mercury tube switch 3 is tilted to closed position. The time necessary for the tilting of the mercury tube switch 3' may be adjusted as shown in detail in Figure 2, by adjusting the connection between the core and the plunger of the dashpot. The energizing of the primary coil of the transformer T energizes the secondary coil'SCand the circuit set up thereby passes through to ignition wires W-W connected in' series therewith. These ignition-wires Ware preferably of nickel-chromium alloy wire flattened and bent back upon itself in the manner shown in said application Serial No. 331,542, also in Figures 4 to 8 inclusive, and when the secondary circuit passes through, will become incandescent so that when the fluid fuel is passed thereover, it will be ignited.

acme-rs The solenoid A is so adjusted that it will not 6 rate to tilt mercury tube switch 3 to close position until after the ignition wires W have become incandescent. The closing of the mercury tube switch 3 closes the circuit from binding post 2 through the switch 3 to the binding post 10. Here the circuit branches, a part of it passing through the electrically operated oil valve or fluid fuel valve V, which is of commercial construction, and is interposed between the source of fluid fuel a'ndthe discharge thereof in the burner nozzle, back to binding post 9 and thence returning to the commercial line. The other portion passes through the heating element 11 of t e safety switch S to the binding post 12 and thence to the motor M and back to the binding post 9 and to the return line of the commercial circuit. It thus seen when the parts are in cold position and the room thermostat closes as shown in Figure 1, the current from the commercial line passes through the safety switch S to the thermal switch TS and through the mercury tube 5 to energize the solenoid A and also the ignition circuit in the transformer T, and a sufiicient time after the closing of this circuit to allow the ignition wires W-W to become incandescent, the circuit acts to 7 the current passing through the closed switch 3, binding post 10, 0 us the oil valve V and a portion passing t rough the heating element 11 and binding post 12 energizes the motor to deliver fuel to the'combustion chamber of the burner and the fuel passed thereinto is ignited by the incandescent wires W. VVhereupon'the heat of combustion acts upon the thermal switch TS causing the mercury tubes 5 and 6 to tilt in the o posite direction, whereby the circuit througli the lower tube 6 is closed before the circuit through the u er switch 5 is broken; The closing of t e ower switch 6 allows a portion of the current passing through the heating element 11 to be shunted out causing the incoming current to pass throu h the safety switch S, binding post 2, and inding post 4, mercury tube switch 6 to binding post 13 and thence to binding post 12 and through the motor M to binding 0st 9 back to the commercial circuit, and a er the closing of the lower switch 6, the thermal switch TS- thereafter breaks the circuit through the upper switch 5 so that the solenoid A. is deenergized as well as the primarycoil of the transformer T, thereby causing switch 3 to open, and deenergize the ignition circuit to the wires w,-w. It is thus seen that the normal running circuit of of the motor of the fuel burning device is completed through the room thermostat, boiler control, binding post 1, safety switch S, binding post 2, inding post i, mercury switch 6, binding-post 13, binding post 12,

operation, a shunt around motor M, and binding post 9, back to the commercial return line.

' the motor will pass from binding post 12 through the element 11 to binding 7 trically operated fuel valve back to binding post 9 and thence to the return of the commercial line, which current is sufiicient to maintain the valve open but not to heat the coil 11 sufficiently to cause release and opening of switch S. I

Should the room thermostat call for heat while the various parts of the device are in the position shown in Figure l and-for some reason or other combustion does not take place, the circuit will continue to pass through room thermostat R, boiler control B, binding post 1, safety switch S, binding post 2, with one portion passing through binding post 4, switch 5, binding post 7, to binding post 8 and a portion through transformer T to binding post 9 and another portion through solenoid A to binding post 9 until the switch 3 is closed and then the other portion from binding post 2 passes through no the switch 3 to binding post 10 and heat coil 11 to binding post 12 and to the motor, and at the same time from binding post 10 through the fuel valve V to binding post 9 from which binding circuit attached thereto pass to the return line to the commercial circuit. The continued passing of the current through the heating element 11 for a predetermined time will release the safety switch S to open the circuit therethrougl1,,and as this switch is connected in the line circuit between the boiler control B and the switches 3 and 5, the circuit is immediately broken through these switches and the operation of the motor ceases. Since safety switch S has been released by the heat element 11, it must be manually returned to closed position, or manually reset, before the motor can again operate. hen the room thermostat calls for heat and the burner operates normally so that combustion occurs, in the manner hereinbefore described, the motor will continue to operate until the desired temperature has been reached which will cause the room thermostat to break the motor circuit and when this occurs, the thermal switch TS will cool and return the switches and 6 to the positions shown in Figure 1, the circuits through the solenoid A and the transformer T having been broken during the normal operation of the burner through the thermal switch TS, all the parts are in the position shown in Figure 1 and are ready to operate again in the normal manner when the room thermostat R calls for heat. 7

f, for any reason, during the normal operation of the burner there is an interruption in the commercial circuit caused by a break in the commercial line, or momentary During the normal post and through the elec post all portions of the pause as' changing from one dynamo to another, if-of suflicient duration, the efiect 1s the same as the opening of the circuit through the room thermostat, so that the thermal switch will cool and, upon resumption of the current, the various parts will act in the same manner as heretofore described when the room thermostat R calls for heat.

t times during the normal operation of the burner combustion will fail'for various reasons, such as a failure of the oil supply or a piece of carbon or dirt clogging the oil valve or air pocket formed i the oil pipe. the former case, unless some safety device was interposed in the motor circuit,;the motor would run continuously until it was discovered that no heat was being produced. In the case of a clogging of the oil valve or an air pocket forming in the oil line, the cause of stoppage might become removed, and in such a case, the resumption of the discharge of the fluid fuel into the heated combustion chamber might have dangerous results, either causing an explosion or if the chamber was of fuel flooded.

According to the construction and arrangement of the parts hereinbefore described, should the fiame fail for any reason after combustion had been initiated, the thermal switch TS will cool and immediatelythe circuitthrough binding. posts 4 and 13 to the motor is broken through switch 6 and the motor will stop. whereupon switch 5 is closed and the circuit passing through binding post 7 to binding post 8 will energize the ignition circuit through the transformer T and solenoid A to close switch 3 so that the incoming current through binding post 1, safety switch S and binding post 2, will pass through switch 3 and binding through heating element-11 to binding post 12, motor M turn line of the commercial source, so that should the failure of fuel to the combustion chamber continue longer, heating coil 11 will release the safety switch S and the motor will immediately stop and cannot be operated again until the safety switch S has been manually reset.

unt1l perhaps the floor would be t hot enough, allow the continual dischar e and binding post 9, to the rcpost 10, and thence The transformer T acts in the manner derelease safety switch S to open is also adjustable as described in my said prior patent. Should the coils of the solenoid A burn out or become disengaged from the circuit, the mer- The time required for the heating element 11 to cury tube switch 3, if not in the open position, will immediately fall to open position and itwould be impossible then to close the circuit to the motor and the device would be inoperative until the damage was repaired. Likewise, should the thermal element of the thermal switch TS burn off or be consumed by the intensity of the heat to which it is subjected, the switches 5 and '6 operated thereby would immediately assume the position shown in Fig. 1 as described in my. said prior pending application 311,436, filed Oct. 10, 1928 now Patent No. 1,762,183, so that the motor circuit would be immediately opened through binding posts 4 and 13 and could not be closed until the damage had been repaired. It being understood that the thermal element of the thermal switch TS is located in such a position as to be acted upon by the heat of combustion, as described in my said prior application just referred to.'

The igniter wires W are preferably of nickel chromium alloy and of sufiicient size throughout theirmajor portion 14 to be of low resistance and that part desired to become incandescent is reduced in cross section by cutting away a lar e longitudinal portion thereof, whereby t e cut away or flattened portion aflords considerably more resistance than the major portions and, therefore, when an electric current passes through the reduced portion it becomes heated and quickly becomes incandescent.

In the type of oil burner shown in Figure 3 it is preferable to employ a plurality of ignition devices and. as shown, they are preferably connected in series with each other in the ignition circuit. In order to cause ignition the igniters must necessarily be located so that the fuel or fuel vapor or combustible mixture to be burned passes over the igniters when they are incandescent, and in most oil burners after ignition occurs, the igniters are not only subjected to the heat of combustion I but also to the products of combustion.

Hot wire ignition systems in which the ignition wire is brought to -Zncandescency by the'passage of current from the commercial line or from the customary commercialv transformer, the ignition wire is subjected to the variations or fluctuations customary in commercial lines. The usual 110 volt commercial electric lighting lines, in some instances, drops as low as 7 5 volts and increases to as much as 140 volts and usually fluctuates from 10 volts above to 10 volts below the standard of 110 volts. These fluctuations are reflected in an ignition wire and sometimes with disastrous results. If the voltage is considerably below 110 volts, the wire does not become incandescent and if it is much above 110 volts, the ignition wire is burned up or destroyed, and in either case ignition does not occur in the time alloted bythe safety device and the burner is shut down. Should the operative.

the ignition wire or completely voltage be too low at the start, to cause ignition when the fuel is first supplied, it may increase suflieiently to bring the igniter to incandescence to cause ignition after the combustion chamber is filled with the fuel vapor and an explosion is the natural result.

In said prior application Serial No. 331,- 542 a hot wire ignition system is disclosed which employs a constant current transformer for the ignition circuit and in which the ignition wires are encased in a protective covering of quartz. The provision of a constant current for the ignition wires insures that they will always e brought to incan descenee during the allotted time, irrespective of the fluctuations of. the commercial current. The casing about the ignition wires was provided to protect the wires from carbon being deposited upon them as well as the deteriorating effects of sulphur in the fuel. The uniform deposit of carbon throughout an ignition wire, as sometimes occurs, reduces the resistance and when connected in circuit withthe commercial line or through the customary transformer and, therefore, the wire ma not become incandescent, the deposit of car 11 upon such a wire in spaced apart portions of the wire, as also sometimes occurs, reduces the resistance through the carbon .covered portions causing an increase in current to pass through the uncovered portions of suflicient intensity to destroy the uncovered portion and thereby rendering the devices in- It has been found that with a constant current transformer supplying the current passing through the ignition wire, constructed as shown herein, that variations in resistance in the secondary circuit is compensated in the same manner as fluctuations in the commercial line or primary circuit, and therefore the depositing of carbon either upon portions of covering the ignitlon wire does not produce the disastrous results as above mentioned.

In accordance with this invention, the larger major portions of the igniter wire 14 are of sufficient size so that the resistance of that part is approximately the same as the resistance of the leads from the transformer. It being impractical to weld the transformer leads, which are customarily of copper, to nickel chromium alloy wire, .the respective ends of the leads andigniter wire are connected by clamping to each other by strip 16 of conducting material supported upon a block 17 of insulating material, as shown in Figures 4, 5 and 6. While the reduced portion 15 of the ignition wire is shown bent back upon itself and the bent back portion then bent at right angles to the major portion '14 of the wire, the reduced portion 15 may be of coil, without departing from the scope of this invention, as long as the major portionl is any other desired shape, such as a resistance or the heat'transmitted from the reduced portion when incandescent, is not sufficient to effect the connection to the transformer leads. The ignition circuit being open after normal combustion of the fuel has been initiated, the ignition Wires thereafter are only subjected to the heat of combustion.

It has been found that during a years operation of an igniter of the form shown that when connected in series, as shown in Figure 3, that the depositing of carbon on one and not upon the other does not impede nor increase the current passing through the other, in fact one may be short-circuited and the other will not be effected. It has also been found that a depositing of carbon on the bent back portions 15, as shown in Figures 4 and 7 will be burned off upon continual usage; In fact the carbon is usually burned off at the first preheat after accumulation occurs.

The formation of the reduced portion 15 of the igniter wire by cutting away of a longitudinal portion in the same plane, as shown in Figures 4 and 7 produces two fiat surfaces when brought close together, so that the area of the adjacent flat surfaces are the same distance apart throughout theirextent with the result that the heat created by the passage of the'ignition current' emanating from the fiat surfaces, not being dissipated in the atmosphere, in the manner of the curved outer surfaces, allows a lower voltage to bring the flattened portion to incandescence.

What I claim is: v

1. In a safety control system for hot wire 1 ignition in electrically operated fluid fuel burners, a room thermostat for automatically controlling the normal operation of the burner motor, a normally closed safety switch, a hot wire ignition device, a constant current transformer, said ignition device in. the seconda ry circuit of constant current of said transformer, a slow acting solenoid, a motor switch operated thereby, an electrically operated slow acting release for the normally closed safety switch, a thermally actuated device responsive to combustion conditions having one switch normally closed and another normally open, and circuits connecting the said elements so that upon closing the. circuit through the room thermostat a preheating circuit is first closed for apredetermined time through the safety switch, normally closed terminal switch, primary of the transformer and windings of the slow acting solenoid erated fluid fuel of combustion the normall open thermal switch closes to close a. circuit from the room thermostat through said closed thermal switch to the motor before the normally closedterminal switch opens and breaks the circuits through the transformer to deenergize the ignition device and solenoid whereupon the motor switch opens and breaks the circuit through the safety release to the motor.

2. A control system for an electrically operated fluid fuel burner of the hot wire ignition type, including a source of commercial electricity having a safety switch therein,-a preheating circuit having a normally closed thermal switch responsive to combustion to open, a slow acting solenoid and a transformer all connected in series to said safety switch, a hot wire igniter in the secondary circuit of the transformer, a starting circuit in parallel with said pre-heating circuit having therein in series a switch actuated to close by said solenoid, a safety switch actuator and a burner motor, a means connected to said solenoid to cause its slow action to delay operation of its switch for a predetermined time, an additional normally open switch responsive to combustion to close before said first switch opens, a running circuit in shunt around the safety switch actuator and having therein said normally open combustion responsive switch.

3. A control system for an electrically opburner of the hot wire ignition type, including a source of commercial electricity pre-heating circuit having a normally closed thermal switch responsive to combustion to open, a slow acting solenoid and a transformer all connected in series to said safety switch, a hot wire igniter in the secondary circuit of the transformer, a'starting circuit in parallel with said pre-heating circuit having therein in series a switch actuated to close by said solenoid, a safety switch actuator and a burner motor, a means connected to said solenoid to cause its slow action to delay operation of its switch for a predetermined time, an additional normally open switch responsive to combustion to close before said first switch opens, a running circuit in shunt around the safety switch actuator, said solenoid operated switch and said transformer and having therein said normally open combustion responsive switch.

IRA. E. MQCABE.

whereby the wires of the ignition device are caused to become incandescent prior to the operation of the solenoid operated motor switch and upon closing the motor switch an additional circuit is closed from the safety switch through the motor switch, motor and safety switch release by which, if combustion fails the safety switch is releasedto open the circuit to the motor, and upon establishment having a safety switch therein, a

CERTIFICATE OF CORREGTIQN.

Patent No. 1,881448. November 29, 1932.

lRA' e. McCABE.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, lines 55 and 69-70. claim 1, for "terminal" read "thermal"; and that the said LettersPatent should be read with this correction therein that thesame may conform to the record of the case in the Patent Office, v

Signed and sealed this 28th day of February, A. D. 1933.

(Seal) M. e, Acting Commissmr of Patents. 

